The use of copper (Cu) metal in multilayer metallization schemes for manufacturing integrated circuits requires the use of a diffusion barrier layer to promote adhesion and growth of the Cu layers and to prevent diffusion of Cu into the dielectric materials. Barrier layers that are deposited onto dielectric materials can include refractive materials, such as tungsten (W), molybdenum (Mo), and tantalum (Ta or TaN), that are non-reactive and immiscible in Cu, and can offer low electrical resistivity.
More recently, ruthenium (Ru) metal has been identified as a potential barrier layer for copper metallization since it is expected to behave similarly to the above-mentioned refractory metals. Furthermore, it is possible that the use of Ru can permit the use of only one layer, as opposed to two layers, such as Ta/TaN. Moreover, current research has suggested that a Ru layer can possibly further replace a Cu seed layer deposited onto the Ta/TaN barrier, and bulk Cu fill by a plating process can proceed directly following Ru deposition. However, a potential drawback to this approach is that a Ru layer can become oxidized if exposed to air or other oxygen-containing ambients and form a RuOx layer prior to the bulk Cu fill process. The presence of a RuOx layer can lead to poor adhesion of the bulk Cu fill layer to the underlying Ru layer, and poor adhesion can result in electro-migration (EM) and stress-migration (SM) problems, as well as poor device production yields. Thus, new processing methods are needed for improving adhesion of Cu to a substrate during integration of Ru layers into Cu metallization schemes.